A typical metal building structure, such as a roof structure or a wall structure, includes a plurality of spaced supporting members, such as purlins, joists or girts, and a series of relatively stiff and rigid interlocked roof or wall panels closing the space between the supporting members. The panels are almost always lapped and sealed, depending upon the length of the roof or wall and the panel length. The prior art fastens lapped joints directly to structural supporting members with hidden clip connectors. A typical prior art clip connector utilizes a base flange having an elongated slot which permits the clip to move relative to the supporting member and with the expansion or contraction of the panels. However, the movement of the clip is limited by the length of the slot. Furthermore, the slot weakens the clip base. Accordingly, this type of clip connector has been found to be deficient in resisting harmful effects of thermal contraction and expansion in addition to certain weaknesses in pull-out strength.